A NEW RECORD OF THE RARE BIVALVE LIMA HAMLINI IN THE PLIOCENE OF LOS ANGELES, CALIFORNIA

by Jack D. Mount¹

Introduction

Recently the State of California started preparations for widening the San Bernardino Freeway as it
passes through the Repetto Hills on the east side of Los Angeles. Last month I visited one of the new road cuts (this habit of checking
out new excavations is one of my more active and profitable pastimes) and was rewarded with a number of specimens of the rather rare
early Pliocene bivalve Lima hamlini Dall. Since I have long been interested in the geology and paleontology of the Repetto Hills,
this find is extra lucky and interesting.

Location

The fossil locality, the largest of the new road cuts, is in the City Terrace area of Los Angeles on
the south side of the San Bernardino Freeway immediately opposite of the campus of the California State College, Los Angeles. The road
cut extends almost the entire length between Eastern Avenue and the Long Beach Freeway (see my geologic map of the area printed last
year in this bulletin (Mount, 1969)). The site is registered in the Department of Geology, California State College, Los Angeles, as
CSCLA Locality 792. The locality is in the Fernando Formation very near the base of that unit. The fossils occur in the dark grey
siltstone at the base of the road out.

This giant Lima was named and described from specimens collected by Homer Hamlin (a Los Angeles
City engineer during the turn of the century) from the Third Street tunnel in downtown Los Angeles.

Fig. 1. Lima
hamlini Dall, x1

Heretofore this Lima has been recorded from the type locality; two localities near the tunnel (now covered by buildings); as
fragmentary remains in outcrops at Malaga Cove and Walteria; and in many oil well cores in the Los Angeles Basin. All these localities
are in the lower part of the Fernando Formation.Lima hamlini is allied to the L. agassizii Dall which lives at a depth of 322 fathoms in
the Gulf of Panama (Woodring,1938). The only other fossils found at CSCLA 792 are small specimens of Delectopecten pedroana
(Trask) which lives today in depths from 10 to 1064 fathoms. Due to the lack of any other species the siltstone was probably deposited
in deep water, some 400 fathoms or more.
The shells of Lima hamlini are very thin, have a silvery sheen and have thin radial ribs which are
subdued or absent on the central part of the valves. It looks as though excavating at the road cut will continue for several more
months. Thus, those of you who are interested in obtaining specimens still have a chance. The fossils are not uncommon but due to the
fragile nature of the valves complete specimens are rare.

References Cited

Dall, W. H., 1900, A new species of Lima: The Nautilus, vol.14, no.2, p.15-16.